1. Field
An apparatus and method for controlling a linear compressor and a linear compressor and a refrigerator having the same are disclosed herein.
2. Background
Compressors typically refer to mechanisms that increases pressure by compressing a refrigerant or other various operating gases, and are widely used in refrigerators and air conditioners. The compressors may be classified into a reciprocating compressor, in which a compression space, into and from which an operating gas, such as a refrigerant, is suctioned and discharged, is formed between a piston and a cylinder and the refrigerant is compressed as the piston linearly reciprocates in the cylinder; a rotary compressor, in which a compression space, into and from which an operating gas, such as a refrigerant, is suctioned and discharged, is formed between an eccentrically-rotatable roller and the cylinder and a refrigerant is compressed as the roller eccentrically rotates along an inner wall of the cylinder; and a scroll compressor, in which a compression space, into and from which an operating gas, such as a refrigerant, is suctioned and discharged, is formed between an orbiting scroll and a fixed scroll and the refrigerant is compressed as the orbiting scroll rotates along the fixed scroll.
The reciprocating compressor may be divided into a recipro type and a linear type according to a method of driving the piston. The recipro type reciprocating compressor employs a method in which a crank shaft is coupled to a rotary motor and a piston is coupled to the crank shaft so as to convert a rotational motion of the rotary motor into a linear reciprocating motion. On the other hand, the linear type reciprocating compressor employs a method in which a piston is directly connected to a mover of a linear motor to perform a reciprocating motion in response to a linear motion of the motor.
The linear type reciprocating compressor does not employ the crank shaft, which converts the rotational motion into the linear motion, and thus, it exhibits less frictional loss and a higher compression efficiency than the recipro type reciprocating compressor. When the reciprocating compressor is used for a refrigerator or an air conditioner, a compression ratio of the reciprocating compressor may be changed by varying a voltage applied to the reciprocating compressor, thereby controlling a cooling capacity (freezing capacity).
FIG. 1 is a block diagram of a compressor control apparatus of a related art reciprocating compressor. As illustrated in FIG. 1, the apparatus for controlling a linear compressor 200 may include a voltage detector 3 to detect a voltage applied to a motor, a current detector 4 to detect a current applied to the motor, a stroke estimator 5 to estimate a stroke based on the detected motor current and motor voltage, and parameters of the motor, a comparator 1 to compare the stroke estimate with a stroke command value to output a difference signal accordingly, and a controller 2 to control the stroke by varying the voltage applied to the motor according to the difference signal.
Hereinafter, an operation of the related art compressor control apparatus will be described.
First, the voltage detector 3 and the current detector 4 detect a motor voltage and a motor current applied to the motor, respectively. The stroke estimator 5 calculates a stroke estimate by applying the motor current, the motor voltage, and parameters of the motor to Equation 1, and applies the calculated stroke estimate to the comparator 1.
                    x        =                              1            α                    ⁢                      ∫                                          (                                                      V                    m                                    -                                      Ri                    m                                    -                                      L                    ⁢                                                                  di                        m                                            dt                                                                      )                            ⁢              dt                                                          [                  Equation          ⁢                                          ⁢          1                ]            
where R denotes resistance, L denotes inductance, and a denotes a motor constant or counter (or back) electromotive force constant.
Accordingly, the comparator 1 compares the stroke estimate with the stroke command value and applies the comparison result to the controller 2. The controller 2 then controls the stroke by varying the voltage applied to the motor according to the difference. That is, the controller 2, as illustrated in FIG. 2, may decrease the motor voltage when the stroke estimate is greater than the stroke command value (S4), and increase the motor voltage when the stroke estimate is smaller than the stroke command value (S5).
A refrigerator as a home appliance runs continuously (24 hours per day), and thus, power consumption of the refrigerator may be a most important technical consideration in the field of refrigerator technology. Efficiency of a compressor may have the greatest influence on the power consumption of the refrigerator, and the efficiency of the compressor should be increased in order to reduce the power consumption of the refrigerator.
One way in which to increase the efficiency of the linear compressor is to reduce frictional loss. To reduce frictional loss, an initial value (or an initial position) of the piston (a location at which the piston is located in the cylinder in an assembled or stopped state) may be moved toward a compression space of the cylinder (or toward a top dead center), so as to decrease a stroke.
However, the initial value of the piston is a factor that determines a maximum cooling capacity. Reduction of the initial value may result in an increase in efficiency of the compressor based on the reduction in frictional loss, but may result in a reduction in the maximum cooling capacity, making it difficult to handle (manage) an overload.
When the initial value of the piston is moved opposite to or away from the compression space, the maximum cooling capacity of the compressor may increase, but a moving distance (a distance between a top dead center and a bottom dead center) of the piston increases. This brings about an increase in frictional loss between the cylinder and the piston, and accordingly, reduces efficiency of the compressor.
The top dead center is abbreviated as “TDC”, and may physically indicate a position of the piston within the cylinder upon completion of a compression stroke of the piston. A point of which the TDC is 0 (TDC=0) (or a point at which a distance from an end of the cylinder (a discharge valve within the cylinder) to an end of the piston is 0) is simply referred to as ‘top dead center.’ Similarly, the bottom dead center is abbreviated as “BDC” and may physically indicate a location upon completion of a suction stroke of the piston.
Consequently, the efficiency of the compressor and the maximum cooling capacity with respect to the initial value of the piston may have a trade-off relationship. Therefore, development of technology for ensuring control stability of the compressor and improving the efficiency of the compressor using the initial value of the piston is necessarily required.